This application relates generally to mechanically assisted circulation (MAC) systems, and more specifically to blood pumps that employ a hollow rotor. The use of a hollow rotor may reduce power consumption via placement of one or more drive magnets close to the outer surface of the hollow rotor thereby resulting in close coupling between the one or more drive magnets and a motor stator used to rotate the hollow rotor.
Ventricular assist devices, known as VADs, often include an implantable blood pump and are used for both short-term (i.e., days, months) and long-term applications (i.e., years or a lifetime) where a patient's heart is incapable of providing adequate circulation, commonly referred to as heart failure or congestive heart failure. According to the American Heart Association, more than five million Americans are living with heart failure, with about 670,000 new cases diagnosed every year. People with heart failure often have shortness of breath and fatigue. Years of living with blocked arteries or high blood pressure can leave a heart too weak to pump enough blood to the body. As symptoms worsen, advanced heart failure develops.
A patient suffering from heart failure may use a VAD while awaiting a heart transplant or as a long term destination therapy. In another example, a patient may use a VAD while recovering from heart surgery. Thus, a VAD can supplement a weak heart (i.e., partial support) or can effectively replace the patient's heart's function. In view of the critical nature of the support provided by a MAC system, it is essential that power supplied to the MAC system not be interrupted for any significant period of time so as to avoid endangering the life of the patient.
VADs can be implanted in the patient's body and powered by an electrical power source inside or outside the patient's body. The power sources used can include alternating current sources such as utility provided electrical power. The use of utility provided power, however, often involves the use of a power cord, which tends to limit the travel freedom of the patient. To enable increased patient travel freedom, patient-worn batteries can be used to power a VAD for a time period limited by the power storage capacity of the batteries and the rate of power consumption by the VAD. Thus, the limits imposed on the travel freedom of the patient are based at least in part on the time period that the VAD can be operated via the patient worn batteries prior to the batteries needing to be recharged. It is therefore desirable for a VAD to have a low power consumption rate (i.e. higher power efficiency) so as to provide a longer time period before the patient-worn batteries need to be recharged.